Smoke point

The smoke point also known as burning point of an oil or fat is the temperature at which, under specific and defined conditions, it begins to produce a continuous bluish smoke that becomes clearly visible.[1] Smoke point values can vary greatly, depending on factors such as the volume of oil utilized, the size of the container, the presence of air currents, the type and source of light as well as the quality of the oil and its acidity content, otherwise known as free fatty acid (FFA) content.[2] The more FFA an oil contains, the quicker it will break down and start smoking.[2][3] The higher in quality and the lower in FFA, the higher the smoke point.[4] It is important to consider, however, that the FFA only represents typically less than 1% of the total oil and consequently renders smoke point a poor indicator of the capacity of a fat or oil to withstand heat.[4][5][6]

The smoke point of an oil correlates with its level of refinement.[7][8] Many cooking oils have smoke points above standard home cooking temperatures:

Hydrolysis and oxidation are the two primary degradation processes that occur in an oil during cooking.[10] Oxidative stability is how resistant an oil is to reacting with oxygen, breaking down and potentially producing harmful compounds while exposed to continuous heat. Oxidative stability is the best predictor of how an oil behaves during cooking .[11][12][13] The Rancimat® method is one of the most common methods for testing oxidative stability in oils.[13] This determination entails speeding up the oxidation process in the oil (under heat and forced air), which enables its stability to be evaluated by monitoring volatile substances associated with rancidity. It is measured as "induction time" and recorded as total hours before the oil breaks down. Canola oil requires 7.5 hours, for example, whereas extra virgin olive oil (EVOO) and virgin coconut oil will last over a day at 110 °C of continuous heat.[9] The differing stabilities correlate with lower levels of polyunsaturated fatty acids, which are more prone to oxidation. EVOO is high in monounsaturated fatty acids and antioxidants, conferring stability.[9]

It has to be noted that the oxidative stability does not correspond to the smoke point and thus the latter cannot be used as a reference for safe and healthy cooking.[14]